We were in Ankarana Reserve in far northern Madagascar, a surreal landscape of exposed karst formations. These are one-of-a-kind formations of permeable rocks, with rivers and streams in between. It’s kind of like Swiss cheese, with water running through it. We were looking for a species of blind cavefish endemic to this region.

But first, we had to make our way through the piles of bat guano [dung]. The cavefishes, which lack pigment and have no eyes, eat some of the invertebrates that are in the water, but a lot of them survive mainly on guano. There are enormous piles of it in these caves, 20- to 30-foot mounds. When you get closer, the mounds seem to come alive, with millions of clicking, rustling cockroaches that run over your feet and up your legs. It’s just like a scene out of an Indiana Jones movie.

Once we got to the water, we snorkeled around to see if we could catch anything. What’s really interesting about the cavefishes is that even though they lack eyes, they’re surprisingly difficult to catch. They’re highly specialized for life in the cave, with elongate snouts bearing well-developed sensory pores and canals, so they have extremely high sensitivity to water movement. They sense you approaching and just dive into the sediment—and once the sediment is stirred up, forget it. But we were lucky to find specimens that turned out to be a new species, with partially developed eyes and some pigment, a light tan.

We nearly missed a great find a few years ago in southwestern Madagascar. There, the limestone runs in massive plateaus that collapse in places creating, sinkholes that must be accessed using climbing gear. I had forgotten my diving mask and went back to the camp with a colleague. By the time we got back, two members of our team who’d been swimming around for an hour in the sinkhole yelled out, “There’s no fish in here. Let’s move on.” But it was a sinkhole like I’d never seen before: deep, relatively clear water. It looked really promising. I couldn’t believe there weren’t any fish there. So I said, “We’ll take a look.”

We went in and swam around for maybe an hour or so, and then I spotted a bizarre looking fish. We stayed in there for nearly three or four hours, and I was able to get two specimens of a new species of blind cavefish, totally different from anything that had been found before, pigmented and dark brown all over, and both anatomically and genetically unique. Although we all got quite sick from swimming in that sinkhole, which is reflected in the species’ name—which translates as “seriously ill” in Malagasy—finding such a strange new fish made it all worthwhile.

A version of this story originally appeared in the Spring issue of Rotunda, the Member magazine.

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